U.S. Secretary of State John Kerry revealed on Friday details of an intelligence report on Syria saying the regime of President Bashar al-Assad carefully prepared for days to launch a chemical weapons attack.

The report said that 1,429 people were killed in the attack, including 426 children, and said the assessment was based on “multiple” streams of intelligence.

Kerry says Syrian regime personnel were at the site of the attack for three days beforehand, making preparations. He says regime elements were told to prepare by putting on gas masks.

Kerry says the United States also knows where the rockets were launched from. He said the rockets came from regime-controlled areas.

Kerry declared Friday that international failure to take military action against the Syrian regime would embolden Iran and Hezbollah.

“This matter also goes beyond the limits of Syria’s borders,” he said.

“It’s about whether Iran, which itself has been a victim of chemical weapons attacks, will now feel emboldened in the absence of action to obtain nuclear weapons. It’s about Hezbollah and every other terrorist group that might contemplate the use of weapons of mass destruction.”

The White House has signaled that Obama, guided by the “best interests” of the United States, was ready to go it alone on Syria after accusing President Bashar al-Assad’s regime of using chemical weapons against its own people.